Field of the Invention
The present invention relates to a toner used for developing an electrostatic image in electrophotography, electrostatic recording, or electrostatic printing.
Description of the Related Art
Toners used in, for example, electrophotography, electrostatic recording, or electrostatic printing are, in a developing step, deposited temporarily on image bearers (e.g., electrostatic latent image bearers) on which electrostatic charge images have been formed. Next, in a transfer step, the thus-deposited toners are transferred from the electrostatic latent image bearers onto transfer media (e.g., transfer paper). Then, the thus-transferred toners are fixed on the media in a fixing step.
At that time, untransferred toners remain as residual toners on latent-image bearing surfaces. Therefore, there is a need to clean the residual toner so as not to disturb the subsequent formation of electrostatic charge images.
Blade cleaning is frequently used in order to clean the residual toners because devices for blade cleaning are simple and good cleanability is capable of being achieved. However, it has been known that the smaller a toner particle diameter is and the closer to spherical a toner shape is, the more difficult it is to clean the residual toners.
Recently, polymerized toners produced by a suspension polymerization method or toners produced by a method called “polymer dissolution suspension method” which is accompanied by volume shrinkage have been put in practical use (see, for example, Japanese Unexamined Patent Application Publication No. 07-152202).
Although the toners produced by the above-described methods are excellent in having a small toner particle diameter, the toners have poor transferability due to a broad particle size distribution. In order to further enhance a transfer efficiency, there is a desire to improve, that is, narrow a particle size distribution of the toners.
The polymerized toners basically include spherical toner particles. Therefore, there has been known a method in which deforming agents (e.g., inorganic fillers and layered inorganic minerals) are allowed to be unevenly distributed on surfaces of toner particles in order to make the toner particles be aspherical (deform the toner particles) in the suspension polymerization method (see, for example, Japanese Unexamined Patent Application Publication Nos. 2005-049858 and 2008-233406).
However, the inorganic fillers and the layered inorganic minerals are difficult to add to particles having small particle diameters in the course of particle formation, so that the particles are likely to be spherical on a smaller particle diameter side. This is because the inorganic fillers and the layered inorganic minerals themselves have particle diameters. As a result, the resultant toner includes particles having a broad shape distribution with different degrees of deformation. In the case of allowing the inorganic fillers and the layered inorganic minerals to be located inside the toner particles, the toner particles are deformed to some extent to improve cleanability. However, leaching out of a release agent or melting out of a binder resin is prevented, resulting in deterioration of low-temperature fixability, hot-offset property, and spreadability.